Cos(arcsin(-1/3)) how to do it by hand?

1. The problem statement, all variables and given/known data
Solve without a calculator
cos(arcsin(-1/3))

3. The attempt at a solution
now i have fount the solution to be (-2/3)(2^(1/2)) now not only did my calculator come up with that but between the SSS formula and pythagorean formula( i think is what we cal it, a^2+b^2....) i was able to get the same answer but the question says not to use a calculator and using those formulas of course im going to have to use a calculator to figure out some of the roots and what not.

I havent had to do this stuff for quite sometime now im a ways past precalc but i was trying to help a friend and im not sure how to do this without a calculator or a root table and any other aids other than my mind. So being that this is precalc i would assume there is a easy way do do this beyond what im trying if the teacher expects it to be done without a calc so if you know how please enlighten me.

It's actually very simple once you know how to do it. Forget about cosine for a moment. Some angle (x) equals the arcsine of -1/3 -- so x=arcsin(-1/3). So you know that the sin(x)=-1/3. Now you can make a right triangle in the IV quadrant and solve for the cosine value, since you are simply solving for the cos(arcsin(-1/3)) or cos(x).

You can do the same and find the general formula to:
sin(arccos(x))
Can you get it? :)

thanks for both of you for the replies. I especially apreciate yours VietDao29, that way seems to be the best route in finding the aswer via no calculator because of its simplicity, i know with the triangle method although easy not so much without the calculator.

thanks for both of you for the replies. I especially apreciate yours VietDao29, that way seems to be the best route in finding the aswer via no calculator because of its simplicity, i know with the triangle method although easy not so much without the calculator.